When a sinner exercises God-given justifying faith, the sinner is engrafted into Christ by the work of the Holy Spirit, the divine agent. The sinner becomes one with Christ who is the object of the sinner’s faith. Only by this union with Christ can the believer now possess “the blessings which God has bestowed on his only begotten Son.”[1] By this intimate union with Christ, the believer becomes one with Him (Eph. 5:30) and Christ unites Himself with us by the work of the Holy Spirit.
Regarding this intimate union with Christ, John Calvin wrote “so long as we are without Christ and separated from him, nothing which he suffered and did for the salvation of the human race is of the least benefit to us. To communicate to us the blessings which he received from the Father, he must become ours and dwell in us. Accordingly… we are said to be engrafted into him and clothed with him, all which he possesses being, as I have said, nothing to us until we become one with him.”[2] Horton has written that this intimate communion between the believer and Christ informed Calvin’s understanding of other theological topics such as the incarnation, the atonement, justification, sanctification, prayer, the church, and the sacraments.[3]
Believers’ union with Christ is consummated by faith, the instrument, and the Holy Spirit does the uniting work as divine agent. Berkhof writes “Every spiritual blessing which believers receive comes to them out of Christ… Subjectively, the union between Christ and believers is effected by the Holy Spirit in a mysterious and supernatural way, and for that reason is generally designated as the unio mystica or mystical union.”[4] Union with Christ is the immediate fruit of faith. Faith is an instrument by means of which one accepts Christ.
The mystical union involves the uniting of Christ and believers as one body, with Christ and the believers ministering to one another. Christ forms the dominating principle in a believer’s life. “Through the Holy Spirit Christ now dwells in believers, unites them to Himself, and knits them together in a holy unity, 1 Cor. 6:17; 12:13; 2 Cor. 3:17, 18; Gal. 3:2, 3.”[5] Christ provides the blessings to the believer and the believer unites with Christ by the conscious exercising of faith through the work of the Holy Spirit.
Thus, union with Christ is a personal and transformative union between Christ and believers whereby believers are changed to the image of Christ and in a sense they suffer and die and are transformed to a new life in Christ. “They share in a measure the experiences of their Lord, Matt. 16:24; Rom. 6:5; Gal. 2:20; Col. 1:24; 2:12; 1 Peter 4:13.”[6]
Faith is made up of three elements. A consideration of these elements shows just how transformative faith is in producing our union with Christ. There is the element of a certain, confident knowledge as a result of the Holy Spirit’s workings through the gospel in the heart of the believer.[7] Then there is the emotional element of faith which is assent which manifests itself in the believer in a conviction of the truth of Christ, an existential need for Christ, and a hungering and thirst for the person of Christ. The third and final element of faith is volition. This involves trust which is a matter of the will. The will directs the soul towards Christ and appropriates Christ to the believer. This is where the believer personally trusts in Christ as his Lord and Savior and acts according to his certain knowledge and conviction by surrendering his soul to Christ and receives and appropriates Christ as the source of spiritual life. Christ is your Lord and Savior so, if Jesus is not the Lord of your life, He is not your Savior.
Believers’ intimate union with Christ is a relationship that is crucial to the next phase of the plan of salvation which is sanctification. Believers walk in union with Christ during the rest of their life after justification growing in the Christian faith and becoming more Christ-like under the influence of this mystical union. This union in Christ transforms believers’ body and soul in the image of Christ.
[1] John Calvin, Institutes of the Christian Religion, Trans, Henry Beveridge (Hendrickson 2008), 348.
[3] Michael Horton, Calvin on the Christian Life, (Crossway 2014), 92.
[4] Louis Berkhof, Systematic Theology (The Banner of Truth Trust, 2021), 461.
[6] Berkhof, 465.
[7] The Heidelberg Catechism, q. 21.
